A metal-air battery uses a metal such as lithium as an anode active material and uses oxygen in the atmosphere as a cathode active material, and is expected, thanks to its high energy density, as a battery capable of obtaining an energy density of 700 Wh/kg required for widespread use and standardization of electric automobiles. This energy density is seven times greater than those of lithium-ion batteries which are presently beginning to be mounted in vehicles.
Patent Document 1 discloses an internal structure of a protected anode of a metal-air battery is provided, as a buffer layer, with a porous resin sheet, for example a separator for a lithium-ion battery (a sheet of porous polyethylene, polypropylene, cellulose, or the like) impregnated with a non-aqueous electrolytic liquid and the like or a protection layer made of a polymer electrolyte and the like in order to prevent direct contact between a solid electrolyte (glass ceramics) and a Li anode. However, there is a problem that if Li deposited on the anode at the time of charging is formed into a fine powder and is dispersed, it becomes impossible to retain Li near the anode current collector and Li does not contribute to charging and discharging, resulting in a decrease in charging and discharging characteristics.
In addition, as disclosed in Patent Document 2, there is a method of suppressing dendrites by maintaining a uniform distance between the cathode and the anode, in which a metal foil laminate material having a high air-tightness is used as an exterior material of the metal-air battery, an air inlet is provided at a position not facing the held surface of the electrode assembly, and a uniform pressure is applied on the cathode. However, even when the dendrite can be suppressed, it is difficult to retain Li at the time of charging near the anode current collector, leaving a problem of how to improve the charging and discharging characteristics.
Moreover, a Li-ion capacitor disclosed in Patent Document 3 has a structure in which both surfaces of a metal Li plate are covered by two separators and end portions of the separators are melted and bonded to seal the metal Li plate. Thus, in the process of pre-doping at an early stage of cell fabrication, the metal Li plate dissolves after the injection of an electrolytic liquid and is dispersed in the electrolytic liquid as Li ions. Here, free small fragments of Li metal are prevented from flowing into the cell, resulting in the prevention of the deterioration in characteristics attributed to e.g. short circuiting.